1. Field of the Invention
The present invention relates to the field of computer system, and more particularly relates to the conservation of power consumption in a computer system.
2. Description of the Related Art
Nowadays personal computers (PC) have so many functions, such as paper processing, briefing making, information searching, entertainment or education, that PCs have become essential equipment in each enterprise and family. However, as it is inconvenient for users to take the PCs along when they go out, portable computers have become a mainstream in the computer industry for their favorable portability.
As mobile computing devices seek to extend time-of-operation between battery charges, efficient power management has became increasingly important. The most common power management system available now is Advanced Configuration and Power Interface (ACPI) that moves the power management completely to the level of the operating system. The power management states defined by the ACPI include: Global system state (G states), Sleep state (S state), Device state (D state) and Central processor unit state (C state).
FIG. 1 is a schematic drawing illustrating four levels of C state, C0 state, C1 state, C2 state and C3 state . In the C0 state , the central processing unit (CPU) executes instructions normally. The C1, C2, and C3 states are different levels of low power states which are sleeping states. According to the usage of the CPU, the operating system drivers the CPU to enter into C1, C2 or C3 state for reducing power consumption.
Specifically, the C3 state offers improved power savings over the C1 and C2 states. Before the CPU enters the C3 state, a command is sent by the OS to disable arbiter of a chip. Moreover, the events for processing aren't transmitted from the chip to the CPU in the C3 state until the CPU returns to the C0 state. After the arbiter of the chip is disabled, the CPU enters the C3 state immediately. While in the C3 state, the CPU's caches maintain state but the CPU is not required to snoop bus master request or CPU accesses to memory.
However, as the bus master request only is sent when the peripheral devices need to access to system memory of the computer system, it is unworthy for the CPU resumes the full performance state for response the bus master request in view of power conservation. Accordingly, conventional power management method can't manage the power consumption of the processor in the most efficient manner, and the usage time of portable computers is reduced which is unfavorable for the users.